Semiconductor structure and method of manufacturing the same

ABSTRACT

The present disclosure provides a semiconductor structure, including an Nth metal layer, a bottom electrode over the Nth metal layer, a magnetic tunneling junction (MTJ) over the bottom electrode, a top electrode over the MTJ, and an (N+M)th metal layer over the Nth metal layer. N and M are positive integers. The (N+M)th metal layer surrounds a portion of a sidewall of the top electrode. A manufacturing method of forming the semiconductor structure is also provided.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims its priority to U.S. provisional patentapplication No. 62/288,793, filed Jan. 29, 2016.

BACKGROUND

Semiconductors are used in integrated circuits for electronicapplications, including radios, televisions, cell phones, and personalcomputing devices. One type of well-known semiconductor device is thesemiconductor storage device, such as dynamic random access memories(DRAMs), or flash memories, both of which use charges to storeinformation.

A more recent development in semiconductor memory devices involves spinelectronics, which combines semiconductor technology and magneticmaterials and devices. The spin polarization of electrons, rather thanthe charge of the electrons, is used to indicate the state of “1” or“0.” One such spin electronic device is a spin torque transfer (STT)magnetic tunneling junction (MTJ) device

MTJ device includes free layer, tunnel layer, and pinned layer. Themagnetization direction of free layer can be reversed by applying acurrent through tunnel layer, which causes the injected polarizedelectrons within free layer to exert so-called spin torques on themagnetization of free layer. Pinned layer has a fixed magnetizationdirection. When current flows in the direction from free layer to pinnedlayer, electrons flow in a reverse direction, that is, from pinned layerto free layer. The electrons are polarized to the same magnetizationdirection of pinned layer after passing pinned layer; flowing throughtunnel layer; and then into and accumulating in free layer. Eventually,the magnetization of free layer is parallel to that of pinned layer, andMTJ device will be at a low resistance state. The electron injectioncaused by current is referred to as a major injection.

When current flowing from pinned layer to free layer is applied,electrons flow in the direction from free layer to pinned layer. Theelectrons having the same polarization as the magnetization direction ofpinned layer are able to flow through tunnel layer and into pinnedlayer. Conversely, electrons with polarization differing from themagnetization of pinned layer will be reflected (blocked) by pinnedlayer and will accumulate in free layer. Eventually, magnetization offree layer becomes anti-parallel to that of pinned layer, and MTJ devicewill be at a high resistance state. The respective electron injectioncaused by current is referred to as a minor injection.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross section of a semiconductor structure, in accordancewith some embodiments of the present disclosure.

FIG. 2 is a cross section of a semiconductor structure, in accordancewith some embodiments of the present disclosure.

FIG. 3 to FIG. 12A are cross sections of a semiconductor structurefabricated in various sequential operations, in accordance with someembodiments of the present disclosure.

FIG. 12B is a cross section of an enlarged portion of the semiconductorstructure of FIG. 12A, in accordance with some embodiments of thepresent disclosure.

FIG. 13A is a cross section of a semiconductor structure fabricated inone operation, in accordance with some embodiments of the presentdisclosure.

FIG. 13B is a cross section of an enlarged portion of the semiconductorstructure of FIG. 13A, in accordance with some embodiments of thepresent disclosure.

FIG. 14 to FIG. 15A are cross sections of a semiconductor structurefabricated in various sequential operations, in accordance with someembodiments of the present disclosure.

FIG. 15B is a cross section of an enlarged portion of the semiconductorstructure of FIG. 15A, in accordance with some embodiments of thepresent disclosure.

FIG. 15C is a top view of an enlarged portion of the semiconductorstructure of FIG. 15B, in accordance with some embodiments of thepresent disclosure.

FIG. 16 is a cross section of a semiconductor structure fabricated inone operation, in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the term “about”generally means within 10%, 5%, 1%, or 0.5% of a given value or range.Alternatively, the term “about” means within an acceptable standarderror of the mean when considered by one of ordinary skill in the art.Other than in the operating/working examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for quantities of materials, durations oftimes, temperatures, operating conditions, ratios of amounts, and thelikes thereof disclosed herein should be understood as modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the present disclosureand attached claims are approximations that can vary as desired. At thevery least, each numerical parameter should at least be construed inlight of the number of reported significant digits and by applyingordinary rounding techniques. Ranges can be expressed herein as from oneendpoint to another endpoint or between two endpoints. All rangesdisclosed herein are inclusive of the endpoints, unless specifiedotherwise.

Embedded MRAM cell in a CMOS structure has been continuously developed.A semiconductor circuit with embedded MRAM cell includes an MRAM cellregion and a logic region separated from the MRAM cell region. Forexample, the MRAM cell region may locate at the center of the aforesaidsemiconductor circuit while the logic region may locate at a peripheryof the semiconductor circuit. Note the previous statement is notintended to be limiting. Other arrangement regarding the MRAM cellregion and the logic region are enclosed in the contemplated scope ofthe present disclosure.

In the MRAM cell region, a transistor structure can be disposed underthe MRAM structure. In some embodiments, the MRAM cell is embedded inthe metallization layer prepared in a back-end-of-line (BEOL) operation.For example, the transistor structures in the MRAM cell region and inthe logic region are disposed in a common semiconductor substrate,prepared in a front-end-of-line operation, and are substantiallyidentical in the aforesaid two regions in some embodiments. The MRAMcell can be embedded in any position of the metallization layer, forexample, between adjacent metal line layers distributed horizontallyparallel to a surface of the semiconductor substrate. For instance, theembedded MRAM can be located between the 4^(th) metal line layer and the5^(th) metal line layer in an MRAM cell region. Horizontally shifted tothe logic region, the 4^(th) metal line layer is connected to the 5^(th)metal line layer though a 4^(th) metal via. In other words, taking theMRAM cell region and the logic region into consideration, the embeddedMRAM occupies a thickness of at least a portion of the 5^(th) metal linelayer and the 4^(th) metal via. The number provided for the metal linelayer herein is not limiting. In general, people having ordinary skillin the art can understand that the MRAM is located between an N^(th)metal line layer and an (N+1)^(th) metal line layer, where N is aninteger greater than or equal to 1.

The embedded MRAM includes a magnetic tunneling junction (MTJ) composedof ferromagnetic materials. A bottom electrode and a top electrode areelectrically coupled to the MTJ for signal/bias conveyance. Followingthe example previously provided, the bottom electrode is furtherconnected to the N^(th) metal line layer, whereas the top electrode isfurther connected to the (N+1)^(th) metal line layer.

Conventional top electrode of an MRAM is manufactured in a non-selectivemanner. Top electrode of the MRAM is in contact with the (N+1)^(th)metal line layer. After the MTJ layer and the top electrode layer arepatterned, a nitride etch stop layer is conformally formed over thepatterned MTJ and the patterned top electrode. An inter layer dielectric(ILD) is then formed surrounding the MRAM, followed by an etch backevenly removing the ILD, the nitride etch stop layer, and a top portionof the top electrode until the top electrode is ensured to be exposedafter the etch back operation. The aforesaid etch back is anon-selective etch back which evenly remove the ILD, the nitride etchstop layer, and the top electrode, rendering a substantially leveledsurfaces for the aforesaid three materials.

During the operation of the non-selective etch back, CF₄ gas and otheretching gases composed of C, H, and F are adopted in an reactive ionetch (RIE). The top electrode is substantially thinned in a main etchstage to ensure the complete exposure of the top electrode. In thisconnection, after the (N+1)^(th) metal line layer is formed to contactwith the top surface of the top electrode, a distance between the(N+1)^(th) metal line and the MTJ (hereinafter “isolation distance”) istoo short to the extent that no proper isolation effect can be rendered.For example, when an MTJ has a diameter of 1000 Å from a top viewperspective, and the isolation distance thereof is smaller than about200 Å, the (N+1)^(th) metal line and the MTJ are considered short,affecting the data storage performance of the MRAM.

On the other hand, after the main etch, a subsequent etch stop layer anda low-k dielectric layer is formed for the preparation of the (N+1)^(th)metal line plating. An over etch is conducted after forming the(N+1)^(th) metal line trench using photolithography operations. The overetch is carried out to expose contact interface between the topelectrode and the (N+1)^(th) metal line in order to electrically couplethe two without sacrificing the isolation effect provided by the topelectrode. A distance between the top surface of the top electrode andthe lowest portion of the (N+1)^(th) metal line in contact with thesidewall of the top electrode (hereinafter “recess distance”) shall bethick enough to render sufficient contact interface for lowering seriesresistance but thin enough to retain proper isolation distance forpreventing electrical short between the (N+1)^(th) metal line and theMTJ.

Adopting the conventional non-selective etch back operation wouldinevitably thin the total thickness of the top electrode. Under suchcircumstances, the isolation distance and the recess distance can be amutually trade-off factor where the increase of the isolation distanceis at the expense of the recess distance thus rendering insufficientcontact interface; and the increase of the recess distance is at theexpense of the isolation distance thus rendering electrical shortbetween the (N+1)^(th) metal line and the MTJ.

The present disclosure provides a semiconductor structure having anMRAM. The thickness of the top electrode of the MRAM is preserved byadopting a selective etch not consuming the top electrode as well as theILD.

In accordance with some embodiments of the present disclosure, asemiconductor structure is provided to have an N^(th) metal layer, abottom electrode over the N^(th) metal layer, a magnetic tunnelingjunction (MTJ) over the bottom electrode, a top electrode over the MTJ,and an (N+M)^(th) metal layer over the N^(th) metal layer. N and M arepositive integers. The (N+M)^(th) metal layer surrounds a portion of asidewall of the top electrode. The top electrode includes a recessregion and an isolation region. The recess region is surrounded by the(N+M)^(th) metal layer whereas the isolation region is defined as theregion from a top surface of the MTJ to a bottom surface of the recessregion, surrounded by a dielectric layer. A ratio of a thickness of therecess region and a thickness of the isolation region is more than about0.5.

In accordance with some embodiments of the present disclosure, asemiconductor structure is provided to have a logic region and a memoryregion. The memory region includes an N^(th) metal layer, a bottomelectrode over the N^(th) metal layer, a magnetic tunneling junction(MTJ) over the bottom electrode, a top electrode over the MTJ, and an(N+1)^(th) metal layer over the top electrode. N is a positive integer.A thickness of the top electrode is more than about 300 Å.

In accordance with some embodiments of the present disclosure, amanufacturing method of the semiconductor structure described herein isprovided.

Referring to FIG. 1A, FIG. 1A is a cross section of a semiconductorstructure 10, in accordance with some embodiments of the presentdisclosure. The semiconductor structure 10 includes a transistorstructure 101 and a metallization structure 101′. In some embodiments,the semiconductor substrate 100 of the transistor structure 101 may bebut is not limited to, for example, a silicon substrate. In anembodiment, substrate 100 is a semiconductor substrate, such as asilicon substrate, although it may include other semiconductormaterials, such as silicon germanium, silicon carbide, gallium arsenide,or the like. In the present embodiment, the semiconductor substrate 100is a p-type semiconductor substrate (P-Substrate) or an n-typesemiconductor substrate (N-Substrate) comprising silicon. Alternatively,the substrate 100 includes another elementary semiconductor, such asgermanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GalnAs, GalnP, and/or GaInAsP; or combinations thereof. In yetanother alternative, the semiconductor substrate 100 is a semiconductoron insulator (SOI). In other alternatives, semiconductor substrate 100may include a doped epi layer, a gradient semiconductor layer, and/or asemiconductor layer overlying another semiconductor layer of a differenttype, such as a silicon layer on a silicon germanium layer. Thesemiconductor substrate 100 may or may not include doped regions, suchas a p-well, an n-well, or combination thereof.

The semiconductor substrate 100 further includes heavily doped regionssuch as sources 103 and drains 105 at least partially in thesemiconductor substrate 100. A gate 107 is positioned over a top surfaceof the semiconductor substrate 100 and between the source 103 and thedrain 107. Contact plugs 108 are formed in inter-layer dielectric (ILD)109, and may be electrically coupled to the transistor structure 101. Insome embodiments, the ILD 109 is formed on the semiconductor substrate100. The ILD 109 may be formed by a variety of techniques for formingsuch layers, e.g., chemical vapor deposition (CVD), low-pressure CVD(LPCVD), plasma-enhanced CVD (PECVD), sputtering and physical vapordeposition (PVD), thermal growing, and the like. The ILD 109 above thesemiconductor substrate 100 may be formed from a variety of dielectricmaterials and may, for example, be an oxide (e.g., Ge oxide), anoxynitride (e.g., GaP oxynitride), silicon dioxide (SiO₂), anitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂), a nitrogen-dopedoxide (e.g., N₂-implanted SiO₂), silicon oxynitride (Si_(x)O_(y)N_(z)),and the like.

FIG. 1 shows a planar transistor having a doped region in thesemiconductor substrate 100. However, the present disclosure is notlimited thereto. Any non-planar transistor, such as a FinFET structure,can have raised doped regions.

In some embodiments, a shallow trench isolation (STI) 111 is provided todefine and electrically isolate adjacent transistors. A number of STI111 is formed in the semiconductor substrate 100. The STI 111, which maybe formed of suitable dielectric materials, may be provided to isolate atransistor electrically from neighboring semiconductor devices such asother transistors. The STI 111 may, for example, include an oxide (e.g.,Ge oxide), an oxynitride (e.g., GaP oxynitride), silicon dioxide (SiO₂),a nitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂), a nitrogen-dopedoxide (e.g., N₂-implanted SiO₂), silicon oxynitride (Si_(x)O_(y)N_(z)),and the like. The STI 111 may also be formed of any suitable “highdielectric constant” or “high K” material, where K is greater than orequal to about 8, such as titanium oxide (Ti_(x)O_(y), e.g., TiO₂),tantalum oxide (Ta_(x)O_(y), e.g., Ta₂O₅), barium strontium titanate(BST, BaTiO₃/SrTiO₃), and the like. Alternatively, the STI 111 may alsobe formed of any suitable “low dielectric constant” or “low K”dielectric material, where K is less than or equal to about 4.

Referring to FIG. 1, a metallization structure 101′ is disposed abovethe transistor structure 101. Because the N^(th) metal layer 121′ maynot be the first metal layer over the transistor structure 101, theomission of a portion of the metallization structure 101′ is representedby dots. An MRAM structure (132, 131, 135, 133) is disposed between anN^(th) metal line 121′ and an (N+1)^(th) metal line 123′. Interconnectstructure includes a plurality of metal layers, namely M₁, M₂ . . .M_(N). Throughout the description, the term “metal layer” refers to thecollection of the metal lines in the same layer. Metal layers M₁ throughM_(N) are formed in inter-metal dielectrics (IMDs) 125, which may beformed of oxides such as un-doped Silicate Glass (USG), FluorinatedSilicate Glass (FSG), low-k dielectric materials, or the like. The low-kdielectric materials may have k values lower than 3.8, although thedielectric materials of IMDs 125 may also be close to 3.8. In someembodiments, the k values of the low-k dielectric materials are lowerthan about 3.0, and may be lower than about 2.5. The N^(th) metal via122 may be formed by a variety of techniques, e.g., electroplating,electroless plating, high-density ionized metal plasma (IMP) deposition,high-density inductively coupled plasma (ICP) deposition, sputtering,physical vapor deposition (PVD), chemical vapor deposition (CVD),low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemicalvapor deposition (PECVD), and the like.

In FIG. 1, the MRAM structure (132, 131, 135, 133) at least includes abottom electrode via (BEVA) 132, a bottom electrode 131, a top electrode133, and an MTJ 135. The BEVA 132 is on the N^(th) metal line 121′. Insome embodiments, a planarization operation, such as a chemicalmechanical polishing (CMP) operation, may be applied to a top surface ofthe BEVA 132. In some embodiments, the BEVA 132 trench possesses atrapezoidal recess surrounded by a dielectric stack 140 including SiCand silicon rich oxide (SRO). Alternatively, the SRO can be replaced orcombined with Tetraethyl Orthosilicate (TEOS). In some embodiments, theBEVA 132 may include conductive materials such as metal. The bottomelectrode 131 may comprise TiN, TaN, W, Al, Ni, Co, Cu or thecombination thereof. In some embodiments, a planarization operation,such as a CMP operation, may be applied to a top surface of the bottomelectrode 131. In some embodiments, the material of the bottom electrode131 is different from that of the BEVA 132. In some embodiments, thethickness of the bottom electrode 131 is in a range from about 100 Å toabout 400 Å.

The MTJ 135 is on the bottom electrode 131. As shown in FIG. 1, asidewall of the MTJ 135 is protected by a dielectric layer 127 such as anitride layer. The top electrode 133 is disposed on the MTJ 135. In someembodiments, the top electrode 133 may include nitrides such as TiN,TaN, Ta or Ru. In some embodiments, the top electrode 133 and the bottomelectrode 131 are made of a same material. In some embodiments, thematerial of the top electrode 133 is different from that of the BEVA 132and the bottom electrode 131.

In FIG. 1, the (N+1)^(th) metal line 123′ is surrounded by dielectriclayer 127 in addition to the IMDs 125. In some embodiments, thedielectric layer 127 includes silicon nitrides. In some embodiments, thedielectric layer 127 includes an SRO layer and an SiC layer, surroundingthe (N+1)^(th) metal line 123′. As shown in FIG. 1, the dielectric layer127 includes a first dielectric layer 127A, a second dielectric layer127B, and a third dielectric layer 127C. The first, the second, and thethird dielectric layers may be composed of same material such as siliconnitride. Since the first, the second, and the third dielectric layersare formed at different deposition operations, interfaces between eachof the dielectric layers can be observed.

In some embodiments, the BEVA 132 of the MRAM structure is electricallycoupled with the doped region. In some embodiments, the doped region isa drain 105 or a source 103. In other embodiments, the BEVA 132 of theMRAM structure 130 is electrically coupled with the gate 107. In someembodiments, the gate 107 of the semiconductor structure 10 can be apolysilicon gate or a metal gate.

As shown in FIG. 1, the (N+1)^(th) metal line 123′ is in contact withthe top surface 133A as well as a portion of the sidewall 133 b of thetop electrode 133. In some embodiments, the top electrode 131 includes arecess region extending from the top surface 133A to a lowest point ofthe (N+1)^(th) metal line 123′, possessing a recess distance R. The topelectrode 131 also includes an isolation region from the bottom of therecess region to a top surface 135A of the MTJ 135, possessing anisolation distance I. In some embodiments, a ratio of the recessdistance R and the isolation distance I is more than about 0.5. That is,the recess thickens R is at least half of the isolation distance I.Given the above discussion, compared to the conventional top electrode,the increase of the recess distance R of the semiconductor structure 10does not affect the isolation effect provided by the isolation region.

In some embodiments, the recess distance R is in a range of from about50 Å to about 150 Å. Conventionally a recess distance R in the aforesaidrange would render insufficient isolation between the (N+1)^(th) metalline and the MTJ because the total thickness of the top electrodeprepared conventionally is thinner than that using the manufacturingmethod described herein. For example, the total thickness of the topelectrode, i.e., the summation of the isolation distance I and therecess distance R, is more than about 300 Å. In some embodiments, theisolation distance I is at least about 200 Å given a diameter D of theMTJ 135 from a top view perspective shown in FIG. 15C to be about 1000Å. In other words, a ratio of the diameter D and the isolation distanceI for some embodiments of the present disclosure is about 5. This ratioguarantees proper isolation between the (N+1)^(th) metal line and theMTJ. Preferably, the aforesaid D/I ratio is smaller than about 5.

Referring to FIG. 1, an inter metal dielectric (IMD) or a dielectriclayer 129 further surrounds the dielectric layer 127. In someembodiments, the dielectric layer 129 is composed of oxides differentfrom the nitrides of the dielectric layer 127. In some embodiments, thedielectric layer 129 includes TEOS. As shown in FIG. 1, a top surface129A of the dielectric layer 129 is higher than the top surface 133A ofthe top electrode 133. Compared to the non-selective main etch to thetop electrode 133, the semiconductor structure 10 provided in thepresent disclosure adopts selective over etch to expose the top surface133A of the top electrode 133. The selective etchants substantially donot consume any of the dielectric layer 129 and the top electrode 133.Hence, the dielectric layer 129 and the top electrode 133 can retain itsoriginal thickness as deposited. In this connection, the dielectriclayer 129 possesses a top surface 129A higher than that of the topelectrode 133.

Referring to FIG. 2, the semiconductor structure 20 can be asemiconductor circuit including a MRAM cell region 100A and a logicregion 100B. Each of the MRAM cell region 100A and the logic region 100Bhas a transistor structure 101 in a semiconductor substrate 100. In someembodiments, the transistor structures 101 are substantially identicalin the MRAM cell region 100A and in the logic region 100B. Details ofthe MRAM cell region 100A can be referred to the description of FIG. 1Aand FIG. 1B. In the logic region 100B, the N^(th) metal line 121′ isconnected to the (N+1)^(th) metal line 123′ by an N^(th) metal via 122of the N^(th) metal layer 121. In some embodiments, the metal lines andmetal vias are filled with electrically conductive material, e.g.copper, gold or another suitable metal or alloy, to form a number ofconductive vias. Metal lines and metal vias in different metal layersform an interconnect structure composed of substantially pure copper(for example, with a weight percentage of copper being greater thanabout 90 percent, or greater than about 95 percent) or copper alloys,and may be formed using the single and/or dual damascene operations.Metal lines and metal vias may be, or may not be, substantially freefrom aluminum. Comparing the MRAM cell region 100A and the logic region100B, a thickness of the MRAM structure 130 is substantially equal to asum of the thickness T2 of the N^(th) metal via 122 and the thickness T1of a portion of (N+1)^(th) metal line 123′. In some embodiments, themetal line 123′ may be the (N+M)^(th) metal line 123′, where M can beany integers greater than 1. In some embodiments, the N^(th) metal line121′ is the fourth metal line and the (N+M)^(th) metal line 123′ is thefifth metal line.

FIG. 3 to FIG. 15B and FIG. 16 are cross-sectional views of asemiconductor structure fabricated at various operations, in accordancewith some embodiments of the present disclosure. In FIG. 3, asemiconductor structure having a predetermined MRAM cell region 100A anda logic region 100B is provided. In some embodiments, a transistorstructure is pre-formed in a semiconductor substrate (not shown in FIG.3). The integrated circuit device may undergo further CMOS or MOStechnology processing to form various features known in the art. Forexample, one or more contact plugs, such as silicide regions, may alsobe formed. The contact features may be coupled to the source and drain.The contact features comprise silicide materials, such as nickelsilicide (NiSi), nickel-platinum silicide (NiPtSi),nickel-platinum-germanium silicide (NiPtGeSi), nickel-germanium silicide(NiGeSi), ytterbium silicide (YbSi), platinum silicide (PtSi), iridiumsilicide (IrSi), erbium silicide (ErSi), cobalt silicide (CoSi), othersuitable conductive materials, and/or combinations thereof. In anexample, the contact features are formed by a salicide (self-alignedsilicide) operation.

An N^(th) metal line 121′ is patterned in a dielectric layer 125 overthe transistor structure. In some embodiments, the N^(th) metal line121′ can be formed of an electroplating operation with a Cu seed layerdeposited over the patterned dielectric layer 125. In other embodiments,the N^(th) metal line 121′ may be formed by a variety of techniques,e.g., electroless plating, high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. A planarizationoperation is performed to expose a top surface of the N^(th) metal line121′ and the top surface of the dielectric layer 125.

In FIG. 4, a dielectric layer 140 in a form of a dielectric stackincluding a SiC layer 141, a TEOS/SRO layer 142, and a SiC layer 141 areblanket deposited over a top surface of the N^(th) metal line 121′ and atop surface of the dielectric layer 125, in both the MRAM cell region100A and the logic region 100B. The dielectric layer 140 can be formedby a variety of techniques, e.g., chemical vapor deposition (CVD),low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), sputtering andphysical vapor deposition (PVD), thermal growing, and the like.

In FIG. 5, a photoresist layer (not shown) is patterned over thedielectric layer 140 to expose a BEVA hole 132′ of the MRAM structure.As shown in FIG. 5, two BEVA holes 132′ are formed in the dielectriclayer 140 by a suitable dry etch operation. In some embodiments, the dryetch in the present operation includes reactive ion etch (RIE) adoptingfluorine-containing gases. In some embodiments, the present dry etchoperation can be any suitable dielectric etch to form via trenches in ametallization structure of conventional CMOS technology. Referring tothe logic region 100B as shown in FIG. 5, the dielectric layer 140 isprotected by the photoresist layer (not shown) such that a top surfaceof the N^(th) metal layer 121′ is not exposed as opposed to thecounterpart in the MRAM cell region 100A.

In FIG. 6, a lining layer 161 is blanket lined over the BEVA holes 132′in the MRAM cell region 100A and over the dielectric layer 140 in thelogic region 100B. Subsequently, in FIG. 7, a deposition of BEVAmaterial 132 is conducted to be disposed over the lining layer 161 andthe dielectric layer 140. In some embodiments, a overfilling of the BEVAmaterial 132 is carried out. The portion overfills the BEVA holes 132′can be a bottom electrode 131 of the MRAM. In some embodiments, the BEVAmaterial 132 includes TiN, TaN, W, Al, Ni, Ta, Ru, Co, Cu or thecombination thereof, deposited by a variety of techniques, e.g.,high-density ionized metal plasma (IMP) deposition, high-densityinductively coupled plasma (ICP) deposition, sputtering, physical vapordeposition (PVD), chemical vapor deposition (CVD), low-pressure chemicalvapor deposition (LPCVD), plasma-enhanced chemical vapor deposition(PECVD), and the like.

In FIG. 8, an MTJ layer is deposited in a form of multiple materialstacks (not illustrated in FIG. 8) over the bottom electrode 131. Insome embodiments, the MTJ layer has a thickness in a range from about150 Å to about 250 Å. The MTJ layer may be formed by variety oftechniques, e.g., high-density ionized metal plasma (IMP) deposition,high-density inductively coupled plasma (ICP) deposition, sputtering,physical vapor deposition (PVD), chemical vapor deposition (CVD),low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemicalvapor deposition (PECVD), and the like. In some embodiments, the MTJ 135may include ferromagnetic layers, spacers, and a capping layer. Thecapping layer is formed on the ferromagnetic layer. Each of theferromagnetic layers may include ferromagnetic material, which may bemetal or metal alloy, for example, Fe, Co, Ni, CoFeB, FeB, CoFe, FePt,FePd, CoPt, CoPd, CoNi, TbFeCo, CrNi or the like. The spacer may includenon-ferromagnetic metal, for example, Ag, Au, Cu, Ta, W, Mn, Pt, Pd, V,Cr, Nb, Mo, Tc, Ru or the like. Another spacer may also includeinsulator, for example, Al₂O₃, MgO, TaO, RuO or the like. The cappinglayer may include non-ferromagnetic material, which may be a metal or aninsulator, for example, Ag, Au, Cu, Ta, W, Mn, Pt, Pd, V, Cr, Nb, Mo,Tc, Ru, Ir, Re, Os, Al₂O₃, MgO, TaO, RuO or the like. The capping layermay reduce write current of its associated MRAM cell. The ferromagneticlayer may function as a free layer whose magnetic polarity or magneticorientation can be changed during write operation of its associated MRAMcell. The ferromagnetic layers and the spacer may function as a fixed orpinned layer whose magnetic orientation may not be changed duringoperation of its associated MRAM cell. It is contemplated that the MTJlayer may include an antiferromagnetic layer in accordance with otherembodiments.

Following the formation of the MTJ layer, a top electrode layer isdeposited over the MTJ layer. The top electrode layer may be formed by avariety of techniques, e.g., high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. In some embodiments,the top electrode layer comprises TiN, TaN, Ta or Ru.

Referring to FIG. 8, a mask layer (not shown) is formed over the topelectrode layer for the ensuing MRAM structure formation. The mask layermay have a multi-layer structure, which may include, for example, anoxide layer, an advanced patterning film (APF) layer and an oxide layer.Each of the oxide layer, the APF layer, and the oxide layer may beformed by a variety of techniques, e.g., high-density ionized metalplasma (IMP) deposition, high-density inductively coupled plasma (ICP)deposition, sputtering, physical vapor deposition (PVD), chemical vapordeposition (CVD), low-pressure chemical vapor deposition (LPCVD),plasma-enhanced chemical vapor deposition (PECVD), and the like. In someembodiments, the mask layer is configured to pattern the MTJ layer toform the MTJ 135, the top electrode layer to form the top electrode 133.In some embodiments, the MTJ 135 and the top electrode 133 are formed byan RIE to have a trapezoidal shape viewing from a cross section.

Subsequently, the first dielectric layer 127A possesses a thickness offrom about 50 Å to about 300 Å is formed over the MTJ 135 and the topelectrode 133. Note a sidewall of the MTJ 135 and the sidewall of thetop electrode 133 are surrounded by the first dielectric layer 127A toprevent oxidation or other contamination. Then, as shown in FIG. 9, thefirst dielectric layer 127A is patterned to expose a top surface of thetop electrode 133 and a portion of the bottom electrode 131. The bottomelectrode 131 is etched and patterned so that two adjacent MRAMs areelectrically decoupled.

In FIG. 10, a second dielectric layer 127B is conformally deposited overthe first dielectric layer 127A, the top electrode 133, and the lininglayer 161. In some embodiments, the second dielectric layer 127B iscomposed of the same materials such as nitrides as the first dielectriclayer 127A. A dielectric layer 129 is further formed to conformallycover the second dielectric layer 127B. Optionally, an antireflectionlayer 130 is leveled over the dielectric layer 129 to facilitate thefollowing photolithography operation.

In FIG. 11, a planarization operation is performed on the antireflectionlayer 130 and the dielectric layer 129 such that the top surface of thedielectric layer 129 is substantially flat across the MRAM cell region100A and the logic region 100B. As shown in FIG. 11, a non-selectiveetch is adopted to remove the dielectric layer 129, the antireflectionlayer 130, and the second dielectric layer 127B using CF_(y)-basedetchant chemistry. y is a positive integer. For example, CF_(y)-basedetchant chemistry includes CF_(y) and other etching gas composed of C,H, and F. In some embodiments, the CF_(y)-based etchant chemistry has aC_(n)H_(l)F_(m):CF_(y) volume ratio in a range of from 0 to about 0.1.In some embodiments, the non-selective etch is carried out under 0% to5% of oxygen gas flow with respect to total gas flow. The non-selectiveetch is performed by end point detection mode so as to stop upon theexposure of the second dielectric layer 127B. Alternatively stated, atthe completion of the non-selective etch, the top surface 133A of thetop electrode 133 is not exposed.

FIG. 12B is a cross section of an enlarged portion of the semiconductorstructure of FIG. 12A. In FIG. 12A, a selective etch is adopted toremove a portion of the second dielectric layer 127B and a portion ofthe first dielectric layer 127A using C_(n)H_(l)F_(m)-based etchantchemistry. n, l, m are positive integers. For example,C_(n)H_(l)F_(m)-based etchant chemistry includes C_(n)H_(l)F_(m) andother etching gas composed of C and F. In some embodiments, theC_(A)H_(l)F_(m)-based etchant chemistry has a CF_(y):C_(n)H_(l)F_(m)volume ratio in a range of from 0 to about 0.1. In some embodiments, theselective etch is carried out under 0% to 10% of oxygen gas flow withrespect to total gas flow. In some embodiments, the C_(n)H_(l)F_(m)includes CH₂F₂, CHF₃, and CH₃F. In FIG. 12B, the result of the selectiveremoval of the first dielectric layer 127A and the second dielectriclayer 127B is enlarged. After the selective etch, the top electrode 133and the dielectric layer 129 retain their original thickness as theselective etchant chemistry consumes the aforesaid two materials in avery low rate.

Note the top surface 133A and the sidewall 133B of the top electrode 133is exposed after the selective etch. However, the selective etch iscontrolled to not expose the sidewall of the MTJ 135. Note in FIG. 11and FIG. 12A, the dielectric stack is removed in the logic region 100Bby proper photolithography operations.

FIG. 13B is a cross section of an enlarged portion of the semiconductorstructure of FIG. 13A. In FIG. 13A, a third dielectric layer 127C isformed to fill the recess produced in the aforesaid selective etch. Thethird dielectric layer 127C also covers a top surface of the dielectriclayer 129. As shown in FIG. 13A, the third dielectric layer 127C coversthe top surface and sidewalls of the top electrode 133. An IMD or alow-k dielectric layer 125 is formed over the MRAM cell region 100A andthe logic region 100B. A step difference 181 can be observed in FIG.13A, therefore, an etch back operation can be optionally performed toobtain a substantially flat top surface for the following trenchformation in both the MRAM cell region 100A and the logic region 100B.The low-k dielectric layer 125 is deliberately kept to act as aprotection layer for the subsequent trench formation. The low-kdielectric layer 125 can prevent the acidic solution from damaging thelow k dielectric layer during a photoresist stripping operation.

In FIG. 13B, the deposition of the third dielectric layer 127C after theselective etch is enlarged for further description. As shown in FIG.13B, an interface between the first dielectric layer 127A and the seconddielectric layer 127B, as well as an interface between the aforesaid twodielectric layer and the third dielectric layer 127C can be observedfrom the cross section because these dielectric layers are deposited indifferent operations. The top surface 133A and a portion of the sidewall133B of the top electrode 133 is again covered by the dielectric layer(i.e., the third dielectric layer 127C), followed by the low-kdielectric layer 125 formation.

In FIG. 14, photoresist (not shown) is patterned over the planarizeddielectric surface to form trenches for metal lines and metal via. Forexample, in the MRAM cell region 100A, a (N+1)^(th) metal line trench123A is formed over the MRAM structure 130, exposing the top surface anda portion of the sidewall of the top electrode 133 of the MRAM. In thelogic region 100B, an N^(th) metal via trench and an (N+1)^(th) metalline trench (combinatory 123B) is formed over the N^(th) metal line121′, exposing a top surface of the Na, metal line 121′.

In FIG. 15B, the MRAM structure in FIG. 15A is enlarged for furtherdescription. As shown in FIG. 15A, conductive metal fills the metal linetrench/metal via trench (hereinafter “trenches”) through, for example, aconventional Dual Damascene operation. The patterned trenches are filledwith a conductive material by an electroplating operation, and excessportions of the conductive material are removed from the surface using achemical mechanical polishing (CMP) operation, an etch operation, orcombinations thereof. Details of electroplating the trenches areprovided below. (N+1)^(th) metal line 123′ may be formed from W, andmore preferably from copper (Cu), including AlCu (collectively, Cu). Inone embodiment, (N+1)^(th) metal lines 123′ are formed using theDamascene operation, which should be familiar to those in the art.First, trenches are etched through the low k dielectric layer. Thisoperation can be performed by plasma etch operation, such as anInductively Coupled Plasma (ICP) etch. A dielectric liner (not shown)then may be deposited on the trenches sidewalls. In embodiments, theliner materials may include silicon oxide (SiO_(x)) or silicon nitride(SiN_(x)), which may be formed by plasma deposition operation, such asphysical vapor deposition (PVD) or chemical vapor deposition (CVD)including plasma enhanced chemical vapor deposition (PECVD). Next, aseed layer of Cu is plated in the trenches. Note the seed layer of Cumay be plated over a top surface of the top electrode 133. Then a layerof copper is deposited in the trenches, followed by planarization of thecopper layer, such as by chemical mechanical polishing (CMP), down tothe top surface of a low k dielectric layer. The exposed copper surfaceand dielectric layer can be coplanar.

In FIG. 15B, the (N+1)^(th) metal lines 123′ is in contact with the topsurface 133A and a portion of the sidewall in proximity to the topsurface 133A of the top electrode 133. A triple point T where the(N+1)^(th) metal lines 123′, the dielectric layer 127, and the topelectrode 133 meet is formed after the formation of the (N+1)^(th) metallines 123′. As previously described in FIG. 1, the recess region havinga recess distance R and the isolation region having an isolationdistance I are defined in the present operation. In some embodiments,the total thickens TE of the top electrode 133 is more than about 300 Å.Other features in FIG. 15B can be referred to those provided in FIG. 1.

FIG. 15C is a top view of a surface dissecting along line AA′ in FIG.15B. It is shown that a diameter D of the MTJ 135, in some embodiments,is about 1000 Å. Under such circumstances, the isolation distance I ofequal to or more than about 200 Å is sufficient to serve the isolationpurpose between the top electrode 133 and the MTJ 135. Along line AA′,the first dielectric layer 127A, and second dielectric layer 127B, andthe dielectric layer 129 or IMD are all shown in FIG. 15C for clarity.In some embodiments, the smaller the diameter D of the MTJ 135, thethinner the isolation distance I is required.

Referring to FIG. 15B and FIG. 15C, since the selective etchantchemistry described above does not consume the top electrode 133 and thedielectric layer 129 in a noticeable manner, the thicknesses of the topelectrode 133 and the dielectric layer 129 can be considered asidentical to its original thickens. Hence, the thickens uniformity ofthe top electrode 133 and the dielectric layer 129 is improved comparedto those obtained by the non-selective etch of the conventionalapproach. A better thickness uniformity of the top electrode 133 and thedielectric layer 129 lead to more uniform the resistance (i.e., smallerresistance variation) of the (N+1)^(th) metal line 123′ due to the factthat the thickness of the (N+1)^(th) metal line 123′ can be effectivelycontrolled via a CMP operation. Alternatively stated, a broader CMPwindow can be adopted in order to obtain desired (N+1)^(th) metal line123′ resistance uniformity. This cannot be achieved by the conventionalapproach where a non-selective etch changes the thicknesses of the topelectrode 133 and the dielectric layer 129 simultaneously.

Referring to FIG. 16, after the planarization operation removing theoverburden of the conductive metal as illustrated in FIG. 15A, an(N+1)^(th) metal line 123′ in both the MRAM cell region 100A and thelogic region 100B, as well as an N^(th) metal via 122 in the logicregion 100B, are formed. Subsequent processing may further includeforming various contacts/vias/lines and multilayer interconnect features(e.g., metal layers and interlayer dielectrics) over the substrate,configured to connect the various features or structures of theintegrated circuit device. The additional features may provideelectrical interconnection to the device including the formed metal gatestructures. For example, a multilayer interconnection includes verticalinterconnects, such as conventional vias or contacts, and horizontalinterconnects, such as metal lines. The various interconnection featuresmay implement various conductive materials including copper, tungsten,and/or silicide. In one example a damascene and/or dual damasceneoperation is used to form a copper related multilayer interconnectionstructure.

Some embodiments of the present disclosure provide a semiconductorstructure. The semiconductor structure includes an N^(th) metal layer, abottom electrode over the N^(th) metal layer, a magnetic tunnelingjunction (MTJ) over the bottom electrode, a top electrode over the MTJ,and an (N+M)^(th) metal layer over the N^(th) metal layer. N and M arepositive integers. The (N+M)^(th) metal layer surrounds a portion of asidewall of the top electrode.

Some embodiments of the present disclosure provide a semiconductorstructure. The semiconductor structure includes a logic region and amemory region. The memory region includes an N^(th) metal layer, abottom electrode over the N^(th) metal layer, a magnetic tunnelingjunction (MTJ) over the bottom electrode, a top electrode over the MTJ,and an (N+1)^(th) metal layer over the top electrode. N is a positiveinteger. A thickness of the top electrode is more than about 300 Å.

Some embodiments of the present disclosure provide a method formanufacturing a semiconductor structure. The method includes forming abottom electrode layer over an N^(th) metal layer, forming a magnetictunneling junction (MTJ) layer over the bottom electrode, forming a topelectrode layer over the MTJ, patterning the top electrode layer and theMTJ layer to form a top electrode and an MTJ, forming a first dielectriclayer surrounding a top surface and a sidewall of the top electrode,forming a second dielectric layer surrounding the top surface and thesidewall of the top electrode, and selectively removing a portion of thefirst dielectric layer and a portion of the second dielectric layer andexposing the top surface and the sidewall of the top electrode.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother operations and structures for carrying out the same purposesand/or achieving the same advantages of the embodiments introducedherein. Those skilled in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1.-20. (canceled)
 21. A semiconductor structure, comprising: an N^(th)metal layer formed over a substrate; a bottom electrode over the N^(th)metal layer; a magnetic tunneling junction (MTJ) over the bottomelectrode; a top electrode over the MTJ; and an (N+M)^(th) metal layerover the N^(th) metal layer, N and M being nonzero, positive integers,wherein the (N+M)^(th) metal layer extends from a first interface withthe top electrode to a second interface with the top electrode, whereinthe first interface is closer a top surface of the substrate than thesecond interface, wherein a dielectric material interfaces anotherportion of the top electrode below the first interface.
 22. Thesemiconductor structure of claim 21, wherein a surface of the topelectrode extending from the first interface to the second interfaceincludes a curvilinear portion of the surface.
 23. The semiconductorstructure of claim 21, wherein the first interface is on a sidewall ofthe top electrode and the second interface is on an uppermost surface ofthe top electrode.
 24. The semiconductor structure of claim 21, whereinthe another portion extends from the first interface to a bottom surfaceof the top electrode.
 25. The semiconductor structure of claim 21,wherein the top electrode comprises TiN, TaN, Ta or Ru.
 26. Thesemiconductor structure of claim 21, wherein the dielectric materialincludes a first dielectric layer and a second dielectric layerinterfacing the another portion of the top electrode wherein a topsurface of the second dielectric layer is higher than a top surface ofthe top electrode.
 27. A semiconductor structure, comprising: a logicregion; and a memory region, comprising: an Nth metal layer; a bottomelectrode over the Nth metal layer; a magnetic tunneling junction (MTJ)over the bottom electrode; a top electrode over the MTJ; and an (N+1)thmetal layer over the top electrode, N being a nonzero, positive integer;an isolation region adjacent the top electrode; and wherein the MTJinterfaces a bottom surface of the top electrode, the (N+1)th metallayer interfaces an uppermost surface of the top electrode and the(N+1)th metal layer interfaces a first region of a surface of the topelectrode extending between the uppermost surface and the bottom surfaceof the top electrode; and the isolation region interfaces a secondregion of the surface of the top electrode, the second region below thefirst region.
 28. The semiconductor structure of claim 27, wherein thefirst region of the surface of the top electrode includes a curvilinearportion.
 29. The semiconductor structure of claim 27, wherein a width ofthe top surface of the top electrode is less than a width of the bottomsurface of the top electrode.
 30. The semiconductor structure of claim27, wherein the top electrode includes titanium or tantalum.
 31. Thesemiconductor structure of claim 27, wherein the logic region comprises:another element of the Nth metal layer; and another element of the(N+1)th metal layer over the Nth metal layer.
 32. A semiconductorstructure, comprising: a semiconductor substrate having a memory regionand a logic region; a first metal line of an Nth metal layer in thememory region and a second metal line of the Nth metal layer in thelogic region; a bottom electrode over the first metal line of the Nthmetal layer, the bottom electrode has a top surface; a magnetictunneling junction (MTJ) over a first portion of the top surface of thebottom electrode; a dielectric layer over a second portion and a thirdportion of the top surface of the bottom electrode, wherein the firstportion interposes the second and third portions of the top surface; atop electrode over the MTJ, the top electrode interfaces the dielectriclayer; and a first metal line of an (N+1)th metal layer over the topelectrode, N being a positive, nonzero integer, wherein a surface of thetop electrode interfaces the (N+1)th metal layer from a first point to asecond point, the second point higher than the first point.
 33. Thesemiconductor structure of claim 32, wherein the dielectric layerinterfaces the bottom electrode from the first point to a third portionbelow the first point.
 34. The semiconductor structure of claim 32,further comprising: a second metal line of the (N+1)th metal layerdisposed over the logic region and connected to the second metal line ofthe Nth metal layer by a via.
 35. The semiconductor structure of claim32, wherein the MTJ is coplanar with the second metal line of the(N+1)th metal layer along a plane defined parallel a top surface of thesemiconductor substrate.
 36. The semiconductor structure of claim 32,wherein a portion of the bottom electrode is coplanar with the via alonganother plane defined parallel the top surface of the semiconductorsubstrate.
 37. The semiconductor structure of claim 32, wherein thedielectric layer is silicon nitride.
 38. The semiconductor structure ofclaim 32, wherein the dielectric layer interfaces the top electrode atthe first point.
 39. The semiconductor structure of claim 32, wherein adistance from the first point to the second point is greater than 0.5times a distance from the first point to a bottom surface of the topelectrode.
 40. The semiconductor structure of claim 32, wherein thefirst point is disposed on a sidewall of the top electrode extending atan inclination with respect to a bottom surface of the top electrode andwherein the second point is disposed on a top surface of the topelectrode extending substantially parallel to the bottom surface of thetop electrode.